I have a series of copy writing jobs. From one post can I hire multiple people for different jobs? In this case do I select 'hire freelancer' each time within that job or when I select 'hire freelancer' does it close the job?

Yes, you can hire multiple freelancer from one job post, but I'd advise posting separate jobs if the job scope and requirements are not the same for each task. That will allow you to manage freelancers much more efficiently if you require them to have different skills for different copywriting tasks.

If you're hiring multiple freelancers, please make sure to check that box before posting the job. Once you hire a freelancer don't check the option to close the job post, so you would keep the job open and be able to hire additional candidates later.

Yes you can edit a job posting after it's posted, you can edit the overview or the details on your job posting. Regarding your questions for hiring multiple freelancers. Once you send a job offer, you will see an option asking if you wanted to keep the job posting open or if you wanted it closed. If you close it you won't be able to hire other freelancers on under the same job posting. I would also like to note that you post the same job posting again.